Light squeezed into atom-sized space by graphene researchers

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By Hilary Lamb

Published Monday, April 23, 2018

Spanish researchers have set a record by fitting light into a space just one atom thick; the smallest confinement possible. The achievement could allow for the development of ultra-small optical devices.

Light is used extensively in communications, from fibre-optic cables to extremely sensitive nanoscale lasers. Much work is dedicated to squeezing light into ever-smaller spaces, allowing for the development of smaller devices. While scientists have demonstrated that metals can be used to compress light, a tricky trade-off between confinement and energy loss has prevented further confinement.

The Graphene Flagship collaboration, led by researchers at the Institute of Photonic Sciences in Barcelona, began by looking for a new approach to exciting graphene plasmons (electron vibrations), which interact strongly with light. They found plasmons could move freely when a layer of graphene was placed closely to an array of metallic rods. Even when this gap between the graphene and metal was reduced to an atom-thick layer of insulator (hexagonal boron nitride), the plasmons were still excited and could move freely.

They discovered that they could control plasmon propagation through the stack of materials simply by applying a voltage.

“Graphene keeps surprising us: nobody thought that confining light to the one-atom limit would be possible,” said Professor Frank Koppens, the quantum nano-optoelectronics expert at the Institute of Photonic Sciences who led the study. “It will open a completely new set of applications, such as optical communications and sensing at a scale below one nanometre.”

The discovery opens up a new field of extreme light-matter interactions for scientific exploration and paves the way for new optical devices on the nanoscale, such as ultra-small optical detectors, sensors and switches.

“While the [Graphene] Flagship is driving the development of novel applications, in particular in the field of photonics and optoelectronics, we do not lose sight of fundamental research,” said Professor Andrea Ferrari, chair of the Graphene Flagship management panel.

“The impressive results reported in this paper are a testimony to the relevance for cutting-edge science of the Flagship work. Having reached the ultimate limit of light confinement could lead to new devices with unprecedented small dimensions.”